MRI technology utilizes magnetism and radio frequency for imaging of patients for medical diagnosis and research. Magnetic resonance imaging device (MRD) design is essentially determined by the type and format of the main magnet, i.e. closed, tunnel-type MRI or open MRI.
In general, three main types of magnets are used in MRI systems: resistive, permanent and superconducting. The most commonly used magnets are superconducting electromagnets. These consist of a coil that has been made superconductive by helium liquid cooling, and further maintained cold by a cryocooler, refrigerator, or liquid nitrogen. Superconducting electromagnets produce strong, homogeneous magnetic fields, but are expensive and require regular maintenance.
Additionally, three gradient MRI magnets are used in the MRI machine to help the imaging process. They are very weak magnets, unlike the others in the system. They create a variable field after the other magnets have been activated and generated a stable field, and are turned on and off very quickly to create different pictures or “slices” for a more thorough and in-depth examination of the patient.
Low field MRI also uses resistive electromagnets, able to create a magnetic field when electricity runs through them. They are cheaper and easier to maintain than superconducting magnets. Resistive electromagnets are far less powerful, use more energy and require a cooling system. Other magnets in use are permanent magnets, of different formats, that are composed of ferromagnetic metallic components. Although they have the advantage of being inexpensive and easy to maintain, they are very heavy and weak in intensity.
Maintaining a uniform and stable magnetic field is a necessity for producing quality imaging. Among the factors affecting this field are temperature, electromagnetic interference, and movement. When referring to small magnetic resonance devices (MRD) the magnet used is usually a permanent magnet. Since a permanent magnet does not produce heat, and being rather small in size the device's heat retention capabilities are low, the MRD is exposed to the environment temperature. Further, being small in size, thus transportable, requires that the MRD will be able to work in different environmental conditions.
Having a large signal to noise ratio (SNR), the MRD needs to be as un-interrupted as possible during the examination. Temperature changes can result in interference in the uniformity of the magnetic field. An MRI scan in a non-uniform magnetic field, results in either artifacts or missed information. Obtaining best results from an MRI scan, and thereby increasing the efficiency of the imaging process requires homogeneity of conditions. As MRI technology is also used for temperature mapping, stabilizing the temperature in which the MRD operates is of importance. Homogeneity of the MRI scanning conditions also enables reliable comparison of MRI scans taken at different times from the same individual or sample, allowing for better monitoring of small changes.
Kruip WO 2000/016116 discloses a mean for stabilization of a magnetic field of a magnetic resonance imaging (MRI) apparatus, generated by permanent magnets, against variation of temperature due to operation of gradient coils. A thermo-conductive plate is positioned between the gradient coils and the permanent magnet, further connected to a temperature sensor and to a plurality of heat pumping devices. However, the system described is an active system, positioned within a magnetic resonance device, and not compatible for small magnetic resonance devices. Moreover, the system describes a mean to maintain temperature change as a result of the operation of the gradient coils and not efficiently built for maintaining temperature changes originating from the external environment. Further, the system described maintains only the heat of the magnet and not the overall temperature of the MRD as a whole. The invention described uses only heat pumping devices and does not utilize any passive temperature regulating systems.
Therefore, there is a need for a passive thermo-regulating assembly providing insulation of the MRD from the external environment, thereby allowing for homogenized imaging conditions. The present invention provides a passive temperature insulating device, placed on the outer side of an MRD, the system is fitting for existing MRDs as well as newly designed ones.